Why does custom tabcontrol disappear after rebuild or clean project?

After I add my new tabcontrol to the form and add controls on tabpages it's ok, Until clean or rebuild the project(Surely build out!)!

when i clean or rebuild the project, every child control is gone and
didn't show on form but it exist on code designer!

my user control source code(tbBody is tabcontrol):

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Drawing;
using System.Data;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

The designer of Form cant't see those TabPag controls to serialize them.

If number of tab pages is not constant

You can remove all items from TabPages collection of the TabControl in your UserControl and let the TabControl initialize without any tab then in your Form, add pages to the TabControl of your UserControl and all tabs and their contents will be serialized because this way the Form designer can see those tabs.

In this solution, you even don't need to call EnableDesignMode for all tab pages.

If number of tab pages is constant

If you have constant count of TabPage you can create public properties in your UserControl and enable designer of each tab page with name of corresponding property.